Effects of beta(2)-agonists on force during and following anoxia in rat extensor digitorum longus muscle

• Fredsted A, Gissel H, Ortenblad N, Clausen T. Effects of beta(2)-agonists on force during and following anoxia in rat extensor digitorum longus muscle. J Appl Physiol 112: 2057-2067, 2012. First published April 5, 2012; doi:10.1152/japplphysiol.01558.2011.-Electrical stimulation of isolated muscles may lead to membrane depolarization, gain of Na+, loss of K+ and fatigue. These effects can be counteracted with beta(2)-agonists possibly via activation of the Na+-K+ pumps. Anoxia induces loss of force; however, it is not known whether beta(2)-agonists affect force and ion homeostasis in anoxic muscles. In the present study isolated rat extensor digitorum longus (EDL) muscles exposed to anoxia showed a considerable loss of force, which was markedly reduced by the beta(2)-agonists salbutamol (10(-6) M) and terbutaline (10(-6) M). Intermittent stimulation (15-30 min) clearly increased loss of force during anoxia and reduced force recovery during reoxygenation. The beta(2)-agonists salbutamol (10(-7)-10(-5) M) and salmeterol (10(-6) M) improved force development during anoxia (25%) and force recovery during reoxygenation (55-262%). The effects of salbutamol on force recovery were prevented by blocking the Na+-K+ pumps with ouabain or by blocking glycolysis with 2-deoxyglucose. Dibutyryl cAMP (1 mM) or theophylline (1 mM) also improved force recovery remarkably. In anoxic muscles, salbutamol decreased intracellular Na+ and increased Rb-86 uptake and K+ content, indicating stimulation of the Na+-K+ pumps. In fatigued muscles salbutamol induced recovery of excitability. Thus beta(2)-agonists reduce the anoxia-induced loss of force, leading to partial force recovery. These data strongly suggest that this effect is mediated by cAMP stimulation of the Na+-K+ pumps and that it is not related to recovery of energy status (PCr, ATP, lactate).

Ämnesord

MEDICIN OCH HÄLSOVETENSKAP  -- Hälsovetenskap -- Idrottsvetenskap (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Health Sciences -- Sport and Fitness Sciences (hsv//eng)

Nyckelord

contractility

salbutamol

theophylline

Na+-K+ pumps

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